The invention relates generally to automatic test equipments, and more particularly to the structural design of remote test heads.
To provide quality assurance, semiconductor device makers systematically perform tests on their products to ensure that they meet or exceed all of their design parameters. Some of the types of tests routinely performed include device parametric testing (a.k.a. DC testing), device logic function testing, and device timing testing (a.k.a. AC testing). The semiconductor device being tested is commonly known as the Device Under Test (DUT) and the test system used in conducting the above tests on the DUT is commonly known as Automatic Test Equipment (ATE). In carrying out the aforementioned tests on very sensitive DUTs, the ATE is necessarily very precise. In general, the ATE hardware is controlled by a computer which executes a test program to present the correct voltages, currents, timings, and functional states to the DUT and monitor the response from the device for each test. The result of each test is then compared to pre-defined limits and a pass/fail decision is made. As such, the ATE hardware normally includes a collection of power-supplies, meters, signal generators, pattern generators, etc. The Pin Electronics (PE) circuitry provides the interface between the ATE and the DUT.
U.S. Pat. No. 4,517,512 to Petrich et al. (hereinafter the ""512 patent) shows an example of a prior art rack-and-stack ATE. As shown in FIG. 1 of the ""512 patent, a control computer including display, power supplies, I/O peripherals (e.g., data storage drives, printers) are stacked on top of each other in a rack console which may be 19 inches wide. The ATE has a remote test head module which carries the instrument cards designed to provide voltages, currents, timings, and functional states to the DUT and to monitor the responses. A cable links the remote test head module to the equipments in the rack console to supply power from the rack console to the remote test head module as well as to allow the transfer of data and control/command signals between the rack console and the remote test head module. During testing, the remote test head module is attached to a test fixture underneath a prober/handler also attached to the test fixture. The prober/handler is used to hold the DUT and to position the DUT relative to the remote test head module. As computers and testers move into the gigahertz range, corresponding wavelengths are a few millimeters. At such wavelengths, almost any wire is an antenna causing signal radiation. Also, ATEs are now working with lower power levels, with currents in the microampere range. This increases the effects of electrical noise. Where higher powers are used to offset noise, transmission line losses occur thereby reducing efficiency. An advantage of this invention is that the distance from the instrument cards in the test head module to the DUT is kept reasonably short to reduce signal radiation, to improve the signal-to-noise ratio, and to reduce transmission line losses.
The instrument cards in the remote test head module are electrically and mechanically connected to each other in a stack-like fashion wherein a male connector on an instrument card is connected to a corresponding female connector on an immediately adjacent instrument card and so on. The connection established by connectors allow the instrument cards to communicate to each other. The instrument cards are connected to the rack console by the cable. The instrument card on top of the stack (a.k.a. the master instrument card) is connected to as many as 64 PE cards. To accommodate 64 PE cards, connectors are arranged in a circle on top of the master instrument card. A disadvantage in connecting instrument cards in a stack is that it does not allow for replacing an instrument card in the stack without disassembling and reconfiguring the instrument card stack. Such disassembly and reconfiguration are likely to result in down time for the ATE which may be undesirable. Another disadvantage in relying on connectors to mechanically connect instrument cards in a stack is that it limits the number of instrument cards that can be stacked and therefore the number of tests that can be carried out by the ATE. While additional mechanical fasteners may be used to secure the instrument cards together thereby allowing more cards to be stacked on top of each other, such fasteners increase costs as well as making it more difficult and time consuming to replace an instrument card.
To accommodate the increase number of tests performed by an ATE (e.g., in linear and mixed signals testing) as well as to improve the ability to replace instrument cards and/or reconfigure the test module rapidly, an approach has been developed wherein instrument cards with connectors are connected to corresponding connectors on a backplane such that the instrument cards are parallel to each other. In so doing, any instrument card can be removed and replaced quickly and easily. A prior art ATE 100 that employs this backplane approach is the ASL1000 that is manufactured by TMT Inc. of Sunnyvale, Calif. which is illustrated in FIG. 1.
As shown in FIG. 1, remote test head module 101 is controlled by central processing unit (CPU) 111 with display monitor 112 and keyboard 113. Power supply 114 supplies the required power to remote test head module 101 which interfaces with DUT 106. Remote test head module 101 includes back plane 102 having up to twenty-one (21) parallel connectors on one side into which twenty-one instrument cards 103 are plugged. To converge the signals from twenty-one proprietary instrument cards 103 into a small test area that interfaces with DUT 106, the opposite side of backplane 102 is connected to system interconnect board 104. On the opposite side of backplane 102, there are six (6) 96-pin connectors 107 to which six corresponding 96-pins connectors 108 of system interconnect board 104 are plugged. System interconnect board 104 is in turn connected to DUT board 105. Accordingly, on the opposite side of system interconnect board 104 there are a plurality of connectors 109 to which corresponding connectors 110 of DUT board 105 are connected.
In this prior art ATE system, any individual instrument card 103 can be easily and rapid replaced. However, when replacement of a large number of instrument cards is involved, it may be necessary to remove interconnect board 104 from backplane 102 (e.g., for reconfiguration). This is quite challenging given the force required to simultaneously disengage/engage all five-hundred-seventy-six (6xc3x9796) pins of six connectors that connect backplane 102 to system interconnect board 104. Accordingly, mechanical assistance may be required. Even with such a mechanical tool, it is still difficult to remove and replace interconnect board 104 rapidly.
Moreover, a test head module that is designed to seat multiple instrument cards like test head module 101 can be rather large in terms of size and weight (as much as 200 lbs) which makes it very difficult to move it close to a DUT let alone maneuvering, even with mechanical aids (e.g., manipulator, wheels, etc.), the test head module in a precise manner to properly connect the test head module with the DUT. As such, it may be necessary to connect PE circuitry to the test head module by a cable to get close to the DUT. This almost always degrades the signals.
Thus, a need exists for an ATE test head module that houses a large number of instrument cards, that allows for rapid reconfiguration of a backplane and replacement of instrument cards, as well as can be placed in close proximity with a DUT without requiring a mechanical manipulator and without requiring strenuous forces in reconfiguring the test head module.
Accordingly, the present invention provides an Automated Test Equipment (ATE) test head module that houses a large number of instrument cards, that allows for rapid reconfiguration of a backplane and replacement of instrument cards, as well as can be placed in close proximity with a DUT without requiring a mechanical manipulator and without requiring strenuous forces in reconfiguring the test head module.
The present invention meets the above objectives with an ATE test head module that comprises a card cage, and a cassette module mechanically joined to the card cage such that the cassette module can be quickly and easily removed from the card cage. The card cage has first backplane (a.k.a. PXI backplane) that is mechanically and electrically connected to a first set of circuit cards such that any card of the first set of circuit cards can be quickly and easily removed from the first backplane. The first backplane is electrically coupled to a Central Processing Unit (CPU).
The cassette module has a second backplane that is mechanically and electrically connected to a second set of circuit cards such that any card of the second set of circuit cards can be quickly and easily removed from the second backplane. The cassette module is designed to hold a Device Under Test (DUT) circuit board for interfacing with a DUT. The first set of circuit cards are in communications with the second set of circuit cards. In an embodiment, the cassette module extends beyond the card cage to form a platform for holding the DUT circuit board. The platform has a cutout with an access door on a rear side allowing access to the second backplane and a through hole in the second backplane to allow visual contact and access to the DUT. Such visual contact is important during various activities such as handler and prober docking, and prober wafer alignment. When closed, the access door prevents light and electrical interference from affecting the DUT.
In one embodiment, the card cage has a cavity and an access opening for accommodating the second set of circuit cards when the cassette module is mechanically joined to the card cage. The first set of circuit cards is industry standard general-purpose instrument cards and the second set of circuit cards are proprietary personality instrument cards conforming to industry standards.
All the features and advantages of the present invention will become apparent from the following detailed description of its preferred embodiment whose description should be taken in conjunction with the accompanying drawings.